1. Field of the Invention
The present invention relates to an optical low-pass filter, a dot matrix-type image display device utilizing the optical low-pass filter, another apparatus utilizing the optical low-pass filter, and an optical component used in the display device.
2. Description of the Background Art
In a dot matrix-type image display device displaying an image by a number of pixels (picture elements) arranged in two dimensions, for example, a liquid-crystal panel, such a phenomenon that so-called sampling noise due to the periodic arrangement of the pixels appears, and degrading the quality of the image is observed.
It has been proposed that a phase grating functioning as an optical low-pass filter is arranged on a display screen of the dot matrix-type image display device in order to reduce or remove the sampling noise (for example, Japanese Patent Laid-Open Publication No. 63-114475). The optical low-pass filter passes spatial frequency components lower than the frequency defined by the pitch between pixels (the pitch between dots) in the dot matrix-type image display device.
When the display screen of the dot matrix-type image display device and the optical low-pass filter are distorted, or are inclined when they are bonded in a state where dust or foreign matter is sandwiched therebetween (the parallel state is not correctly kept), rainbow-shaped interference fringes occur, resulting in lowered reproducibility of the image.
A liquid-crystal panel which is a representative of the dot matrix-type image display device is applied to electronic equipment such as a view finder of a video camera and a portable television. The electronic equipment require such miniaturization that they are easy to carry and require reduction in cost. In order to miniaturize the liquid-crystal panel and simplify the assembling processes thereof, it is desired that the liquid-crystal panel and the optical low-pass filter are joined and integrated. It is one of inevitable technical problems to prevent the above described occurrence of the interference fringes in this case.
On the other hand, the grating thickness of the optical low-pass filter requires fabrication precision on the order of 0.01 .mu.m, whereby the fabrication thereof is difficult and the yield thereof is bad.
Furthermore, in a liquid crystal display device using an STN (Super Twisted Nematic) liquid crystal, a phase plate is required to convert elliptically polarized light into linearly polarized light to improve the contrast. If the phase plate and an optical low-pass filter are further mounted on the liquid crystal display device, the structure of the liquid crystal display device is forced to be complicated.